Many integrated circuit devices include digital circuitry formed of metal-oxide-semiconductor (MOS) transistor devices, which are built using complementary MOS (CMOS) fabrication processes optimized for high-density, high-speed N-channel and P-channel MOS transistors. Such high-density circuitry is common in modern consumer electronic products such as wireless communications devices, portable computers, etc., in which digital circuitry is powered by batteries. In such products, it is generally desirable to provide a maximum amount of functionality in a limited amount of space, while keeping power consumption and cost to a minimum. To optimize circuit functionality, area, and power consumption, transistor sizes are often minimized and the transistors are designed to operate at low voltage levels. However, some electronic devices require transistor devices that operate at voltages substantially higher than that of logic or memory transistors. Such transistor devices are referred to as high voltage transistor devices and can be employed for power related tasks, such as power source switching.
One suitable type of high voltage transistor device is a drain-extended metal-oxide-semiconductor (DEMOS) transistor device using N or P channels. DEMOS devices advantageously combine short-channel operation with high current handling capabilities, relatively low drain-to-source on-state resistance (Rdson), and the ability to withstand relatively high drain-to-source voltages without suffering voltage breakdown failure, where DEMOS device designs often involve a tradeoff between breakdown voltage (BVdss) and Rdson. In addition to performance advantages, DEMOS device fabrication is relatively easy to integrate into CMOS process flows, facilitating use in devices where logic, low power analog, or other circuitry is also to be fabricated in a single integrated circuit (IC). These DEMOS devices employ an extended drain region having the same dopant type as the drain region. As a result of the extended drain region, the drain to source voltage for such devices is increased, at least partially according to a length of this extended drain region.
As stated above, it is generally desired to minimize or reduce area consumption for transistor devices. However, reducing area consumption for drain extended transistor devices can be at odds with providing a high enough operating voltage.